Methods and systems for deploying optical fiber

ABSTRACT

There are described methods and systems for deploying optical fiber within a conduit. In one aspect, an optical fiber injector comprising a pressure vessel having a fluid inlet and a fluid outlet. The fluid outlet is engaged with an open end of the conduit. A length of optical fiber is provided within the pressure vessel. The optical fiber is then jetted into the conduit by injecting a fluid into the pressure vessel via the fluid inlet. The optical fiber injector is configured such that the fluid is directed from the fluid inlet to the fluid outlet, and urges the optical fiber to move through the conduit, thereby deploying the optical fiber within the conduit. In a further aspect, there is provided a modular assembly comprising a pipeline and a line of two or more conduits arranged end-to-end. Each pair of opposing ends of adjacent conduits is connected together by a separate splice box. The line is positioned along and adjacent to a length of the pipeline.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority to U.S. Ser.No. 16/485,917 filed on Aug. 14, 2019, which is a U.S. National Stageentry of PCT/CA2018/050152 filed Feb. 9, 2018, which claims priority tonow abandoned U.S. provisional application Ser. No. 62/458,967 filedFeb. 14, 2017, entitled “Methods and Systems for Deploying OpticalFiber,” the contents of which are incorporated herein by reference inits entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to methods and systems for deployingoptical fiber. In particular, the disclosure relates to a modularassembly for deploying optical fiber along a pipeline, and to a methodand system including an optical fiber injector for deploying opticalfiber within a conduit.

BACKGROUND TO THE DISCLOSURE

Production and transportation of oil and gas generally involvestransporting the oil and gas along various types of channels. Forexample, during conventional oil and gas production, oil and gas arepumped out of a formation via production tubing that has been laid alonga wellbore; in this example, the production tubing is the channel.Similarly, when fracking is used to produce oil and gas, the well inwhich the fracking is performed is the channel. As another example, oiland gas, whether refined or not, can be transported along a pipeline; inthis example, the pipeline is the channel. In each of these examples,acoustic events may occur along the channel that are relevant to oil andgas production or transportation. For example, the pipeline or theproduction tubing may be leaking, and during fracking new fractures maybe formed and existing fractures may expand. Each such event is anacoustic event as it makes a noise while it is occurring. It canaccordingly be beneficial to detect the presence of these types ofacoustic events.

One method of detecting the presence of such acoustic events is throughthe use of optical fibers. By using optical interferometry, fiber opticcables can be deployed downhole for the detection of acoustic events inchannel housing used for the production and transportation of oil andgas. Optical interferometry is a technique in which two separate lightpulses are generated: a sensing pulse and a reference pulse. Thesepulses may be generated by an optical source such as a laser. Whenoptical interferometry is used for fiber optic sensing applications, thesensing and reference pulses are at least partially reflected backtowards an optical receiver and interfere with each other resulting inan interference signal. The interference signal can then be analysed togather information on the acoustic event.

Installation of long-distance optical fiber can be an expensive process.For example, the process of installation of the optical fiber mayinterfere with the installation of the pipe itself; the fiber opticcables may be damaged while heavy equipment is being used to install thepipe segments; different segments of the pipe may not be easilyaccessible (such as segments that are installed using horizontaldirectional boring). In addition, current methods of optical fiberinjection typically suffer from range issues. Optical fiber can beinjected into a conduit for relatively short distances (a few hundredmeters), but for longer distances, or in cases where the installationpath is not straight and contains bends and twists, the forces offriction can easily overcome the force of the equipment used to jet theoptical fiber.

There is therefore a need in the art for improvements in the way inwhich optical fiber can be installed or deployed within a conduit. Thepresent disclosure seeks to address such needs.

SUMMARY OF THE DISCLOSURE

In a first aspect of the disclosure, there is provided a method ofdeploying optical fiber within a conduit, comprising: providing anoptical fiber injector comprising a pressure vessel having a fluid inletand a fluid outlet; engaging the fluid outlet with an open end of aconduit; providing a length of optical fiber within the pressure vessel;and jetting the optical fiber into the conduit by injecting a fluid intothe pressure vessel via the fluid inlet, wherein the optical fiberinjector is configured such that the fluid is directed from the fluidinlet to the fluid outlet, and urges the optical fiber to move throughthe conduit, thereby deploying the optical fiber within the conduit.

The pressure vessel may be sealed during jetting of the optical fiber.Sealing of the pressure vessel may comprise ensuring that no fluid mayflow into or out of the pressure vessel except via the fluid inlet andfluid outlet.

The fluid may comprise compressed air or a liquid, such as water whichmay be combined with an amount of antifreeze. The buoyancy of a liquidsuch as water may further assist in deployment of the optical fiberwithin the conduit.

The optical fiber may be attached to an optical fiber piston movablethrough the conduit. The optical fiber injector may be configured suchthat, during jetting of the optical fiber, the fluid urges the opticalfiber piston to move through the conduit, thereby assisting deploymentthe optical fiber within the conduit. The optical fiber piston may havea width similar to a width of an internal bore of the conduit, such thatthe optical fiber piston may act substantially as a piston duringjetting of the optical fiber. Prior to jetting the optical fiber, theoptical fiber piston may be positioned in the open end of the conduit(i.e. the open end of the conduit that is engaged with the fluidoutlet).

Prior to providing the length of optical fiber in the pressure vessel, apull string comprising a flexible elongate member may be deployed in theconduit. Deploying the pull string may comprise: providing a pull stringinjector comprising a pressure vessel having a fluid inlet and a fluidoutlet; engaging the fluid outlet with the open end of the conduit;providing the pull string in the pressure vessel, the pull string beingattached to a pull string piston movable through the conduit; andjetting the pull string into the conduit by injecting a fluid into thepressure vessel via the fluid inlet, wherein the pull string injector isconfigured such that the fluid is directed from the fluid inlet to thefluid outlet and urges the pull string piston to move through theconduit, thereby deploying the pull string within the conduit. Theoptical fiber injector may be the pull string injector.

Prior to jetting the pull string, the pull string piston may bepositioned in the open end of the conduit.

The pull string piston may have a width similar to a width of aninternal bore of the conduit, such that the pull string piston may actsubstantially as a piston during jetting of the pull string.

After jetting the pull string and prior to jetting the optical fiber,the optical fiber piston may be attached to the pull string. Duringjetting of the optical fiber, the pull string may be retracted from anopposite open end of the conduit so as to impart a tensile force on theoptical fiber.

The optical fiber injector may further comprise a spool on which iswound the optical fiber. The method may further comprise rotating thespool during jetting of the optical fiber so as to unwind the opticalfiber from the spool.

The optical fiber may be comprised in optical fiber cable. The opticalfiber cable may comprise one or more additional fibers for increasing arigidity of the optical fiber cable.

The optical fiber may be comprised in optical fiber cable. The opticalfiber cable may be provided with a coating for increasing a lubricity ofthe optical fiber cable.

During jetting of the optical fiber, suction may be applied at an openend of the conduit opposite the open end engaged with the fluid outlet,thereby further assisting deployment the optical fiber within theconduit.

In a further aspect of the disclosure, there is provided an opticalfiber injector for deploying optical fiber within a conduit, comprising:a pressure vessel having a fluid inlet and a fluid outlet adapted toengage with an open end of a conduit; a spool for having optical fiberwound thereon; and a drive mechanism coupled to the spool and configuredwhen operating to cause the spool to rotate and thereby unwind opticalfiber therefrom.

The optical fiber injector may further comprise a length of opticalfiber wound on the spool.

The optical fiber injector may be a completely contained pressure vesselthat allows the entire spool of optical fiber to be under fluidpressure, such that substantially all of the fluid energy is harnessedfor moving the optical fiber within the conduit, eliminating the needfor drive tractors and/or compression air fittings.

The optical fiber may be attached to an optical fiber piston movablethrough the conduit.

The optical fiber injector may further comprise a transparent portionfor observing whether optical fiber is moving from the spool towards thefluid outlet.

In a further aspect of the disclosure, there is provided an opticalfiber deployment system comprising: a conduit; an optical fiber injectorcomprising a pressure vessel having a fluid inlet and a fluid outlet,the fluid outlet being engaged with an open end of the conduit; a lengthof optical fiber in the pressure vessel; and a fluid injector forinjecting fluid into the pressure vessel, wherein the fluid injector isfluidly coupled to the fluid inlet and is configured to inject fluidinto the pressure vessel such that the fluid is directed from the fluidinlet to the fluid outlet, and urge the optical fiber to move throughthe conduit, thereby deploying the optical fiber within the conduit.

The pressure vessel may be sealed during injection of the fluid. Sealingof the pressure vessel may comprise ensuring that no fluid may flow intoor out of the pressure vessel except via the fluid inlet and fluidoutlet.

The fluid injector may comprise a compressor configured to injectcompressed air into the pressure vessel. The fluid may comprise a liquidsuch as water which may be combined with an amount of antifreeze. Thebuoyancy of a liquid such as water may further assist in deployment ofthe optical fiber within the conduit.

The optical fiber may be attached to an optical fiber piston movablethrough the conduit. The optical fiber injector may be configured suchthat, during injection of the fluid, the fluid urges the optical fiberpiston to move through the conduit, thereby assisting deployment of theoptical fiber within the conduit.

The system may further comprise a pipeline or a wellbore in acousticproximity to the conduit. Thus, the optical fiber may be deployedadjacent a wellbore casing, for example, before or during downholedrilling operations.

The optical fiber injector may further comprise a spool on which iswound the optical fiber. The system may further comprise a drivemechanism coupled to the spool and configured when operating to causethe spool to rotate and thereby unwind the optical fiber from the spool.

A pull string comprising a flexible elongate member may be deployedthrough the conduit. The pull string may be attached to the opticalfiber piston.

The system may further comprise a retractor coupled to the pull stringand configured when operating to retract the pull string from anopposite open end of the conduit so as to impart a tensile force on theoptical fiber.

The system may further comprise a suction device configured, duringinjection of the fluid, to apply suction at an open end of the conduitopposite the open end engaged with the fluid outlet, thereby furtherassisting deployment the optical fiber within the conduit.

In a further aspect of the disclosure, there is provided a modularassembly for deployment of optical fiber along a pipeline, the modularassembly comprising: a pipeline; and a line of two or more conduitsarranged end-to-end, each pair of opposing ends of adjacent conduitsbeing connected together by a separate splice box, wherein the line ispositioned along and adjacent to a length of the pipeline.

The modular assembly may further comprise an optical fiber disposedwithin each of the conduits.

The modular assembly may allow an operator to replace a section of fiberthat has become damaged, without having to replace the entire length offiber. By using conduits, the risks during fiber installation arereduced, i.e. the installation crew do not need to worry about thedelicate fiber during the pipeline installation. The conduit may besimply placed inside a trench, and fiber can be installed at a laterdate.

The optical fibers disposed within each pair of adjacent conduits may beoptically connected together via the splice box connecting together thepair of adjacent conduits so as to form a light path through the line.The optical fiber disposed within each of the conduits may comprise atleast one pair of fiber Bragg gratings. The modular assembly may furthercomprise an optical interrogator optically coupled to the optical fiberdisposed within the conduit at an input end of the line. The opticalinterrogator may be operable to transmit light into the optical fiberdisposed within the conduit at the input end, and the opticalinterrogator may be operable to receive from the optical fiber disposedwithin the conduit at the input end the transmitted light which has beenreflected by the at least one pair of fiber Bragg gratings.

The modular assembly may further comprise an absorption unit opticallycoupled to the optical fiber disposed within the conduit at anabsorption end of the line. The absorption unit may be operable toabsorb light output from the optical fiber disposed within the conduitat the absorption end so as to prevent the output light reflecting backinto the optical fiber disposed within the conduit at the absorptionend.

The modular assembly may further comprise an additional optical fiberdisposed within each of a plurality of the conduits. The plurality mayform an unbroken portion of the line and may include the conduit at theinput end. The additional optical fibers may be optically connectedtogether via the splice boxes connecting together the plurality of theconduits so as to form an additional light path through at least aportion of the line. The additional optical fiber disposed within theconduit at the input end may be optically coupled to the opticalinterrogator.

Multiple service fibers also allow the modular assembly to be morerobust; for example if the sensing fiber in one zone is cut off, theremainder of the sensing optical fiber, in other conduits, may stilloperate. In addition, service fibers help provide separate travel pathsfor the light travelling to different segments of the conduits. Thus,light that travels to a conduit segment that is more distant from theinterrogator does not have to travel through the previous conduitsegments' sensing fiber (as it travels instead through that particularconduit segment's service fiber) and is thus not attenuated by the FBGsof the previous conduit's sensing fiber. In addition, service fibers mayreduce the optical collisions between the light packets traveling in thedifferent conduits. The service fibers may act as dedicated lead-in andlead-out fibers to each conduit, and may ensure that the interrogatorcan launch light into, and receive light back from, each conduit withoutthat light having to travel through any previous conduit's sensingfiber.

The plurality of the conduits may include all of the conduits of theline. The additional optical fiber disposed within the conduit at theabsorption end may be optically coupled to the absorption unit.

At least one of the splice boxes connecting together a pair of adjacentconduits may comprise a circulator. The one conduit of the pair ofadjacent conduits closest an input end of the line may comprise alead-in optical fiber and a separate return optical fiber. The lead-inand return optical fiber may be optically coupled to the circulator. Theone conduit of the pair of adjacent conduits closest an absorption endof the line may comprise a sensing optical fiber optically coupled tothe circulator and comprising a pair of fiber Bragg gratings. Thecirculator may be operable to direct light from the lead-in opticalfiber to the sensing optical fiber, and to direct light reflected by thepair of fiber Bragg gratings from the sensing optical fiber to thereturn optical fiber.

The modular assembly may further comprise an optical interrogator havinga transmission coupler and a receiver coupler, the transmission couplerbeing optically coupled to the lead-in optical fiber such that theoptical interrogator is operable to transmit light into the lead-inoptical fiber, and the receiver coupler being optically coupled to thereturn optical fiber such that the optical interrogator is operable todetect from the return optical fiber the transmitted light reflected bythe pair of fiber Bragg gratings.

An additional one of the splice boxes connecting together an additionalpair of adjacent conduits may comprise an additional circulator. The oneconduit of the additional pair of adjacent conduits closest an input endof the line may comprise an additional lead-in optical fiber and aseparate additional return optical fiber. The additional lead-in andadditional return optical fibers may be optically coupled to theadditional circulator. The one conduit of the additional pair ofadjacent conduits closest an absorption end of the line may comprise anadditional sensing optical fiber optically coupled to the additionalcirculator and comprising an additional pair of fiber Bragg gratings.The additional circulator may be operable to direct light from theadditional lead-in optical fiber to the additional sensing opticalfiber, and may be operable to direct light reflected by the additionalpair of fiber Bragg gratings from the additional sensing optical fiberto the additional return optical fiber.

At least one of the conduits of the line may be divided into multipleseparate channels. Each channel may be dimensioned to carry a separateoptical fiber.

One of the conduits of the line may comprise a rod or tape releasablyfixed to an internal surface of the one conduit.

Each conduit may be made from a stainless steel capillary tube. Eachconduit may be made from high-density polyethylene, and may comprisedual or multi-duct versions of the conduits found athttp://www.duraline.com/content/futurepath.

The line may be positioned within one meter of the length of thepipeline.

The line may be fixed to an outer surface of the length of the pipeline.

In a further aspect of the disclosure, there is provided a method fordeploying optical fiber along a pipeline, the method comprising:installing a modular assembly along and adjacent to a length of thepipeline, the modular assembly comprising a line of two or more conduitsarranged end-to-end, each pair of opposing ends of adjacent conduitsbeing connected together by a separate splice box; disposing opticalfiber within each conduit of the installed modular assembly; andoptically connecting together the optical fibers disposed within eachpair of adjacent conduits via the splice box connecting together thepair of adjacent conduits.

Installing the modular assembly may comprise coupling the modularassembly to the length of the pipeline prior to installation of thepipeline such that the modular assembly is installed with the pipeline.

Installing the modular assembly may comprise positioning the modularassembly within one meter of the length of the pipeline after thepipeline has been installed.

Installing the modular assembly may comprise fixing at least one conduitof the modular assembly to an outer surface of the length of thepipeline.

Disposing optical fiber into each conduit may comprise pushing at leastone optical fiber through at least one conduit using a cable-jettingdevice or a spooling device.

Disposing optical fiber into each conduit may comprise pulling at leastone optical fiber through at least one conduit using a rod or tape. Therod or tape may be connected to the at least one optical fiber andextends through a majority of the at least one conduit.

The rod or tape may be releasably fixed to an internal surface of the atleast one conduit prior to being used to pull the at least one opticalfiber through the at least one conduit.

The disposing of optical fiber into at least one of the conduits may becarried out using any of the above-described methods.

The method may further comprise disconnecting an optical fiber disposedwithin one of the conduits from the splice boxes connected at either endof the one conduit; removing the disconnected optical fiber from the oneconduit; disposing a replacement optical fiber within the one conduitand optically connecting the replacement optical fiber to the spliceboxes connected at either end of the one conduit.

The method may further comprise determining that the optical fiber ismalfunctioning prior to disconnecting the optical fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure will now be described in conjunction withthe accompanying drawings of which:

FIG. 1 is a block diagram of a system for processing acoustic data froma pipeline, which includes an optical fiber with fiber Bragg gratings(“FBGs”) for reflecting a light pulse;

FIG. 2 is a schematic that depicts how the FBGs reflect a light pulse;

FIG. 3 is a schematic that depicts how a light pulse interacts withimpurities in an optical fiber that results in scattered laser light dueto Rayleigh scattering, which is used for distributed acoustic sensing(“DAS”);

FIG. 4 is a schematic of a modular assembly for deploying optical fiberalong a pipeline, in accordance with an embodiment of the disclosure;

FIG. 5 is a schematic of a modular assembly comprising multiple opticalfibers, in accordance with an embodiment of the disclosure;

FIG. 6 is a schematic of a method of deploying optical fiber within aconduit, in accordance with an embodiment of the disclosure;

FIG. 7 is a schematic of a method of deploying optical fiber within aconduit, in accordance with an embodiment of the disclosure;

FIG. 8 is a perspective view of an optical fiber injector, in accordancewith an embodiment of the disclosure;

FIG. 9 is a schematic of the optical fiber injector in operation;

FIG. 10 is a schematic of an optical fiber injector and an optical fiberretractor deploying optical fiber within a conduit, in accordance withan embodiment of the disclosure; and

FIG. 11 is a flowchart illustrating a method of deploying optical fiberwithin a conduit, in accordance with an embodiment of the disclosure.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The present disclosure seeks to provide improved methods and systems fordeploying optical fiber. While various embodiments of the disclosure aredescribed below, the disclosure is not limited to these embodiments, andvariations of these embodiments may well fall within the scope of thedisclosure which is to be limited only by the appended claims.

Referring now to FIG. 1, there is shown one embodiment of a system 100for fiber optic sensing using optical fiber interferometry. The system100 comprises an optical fiber 112, an interrogator 106 opticallycoupled to the optical fiber 112, and a signal processing device(controller) 118 that is communicative with the interrogator 106. Whilenot shown in FIG. 1, within the interrogator 106 are an optical source,optical receiver, and an optical circulator. The optical circulatordirects light pulses from the optical source to the optical fiber 112and directs light pulses received by the interrogator 106 from theoptical fiber 112 to the optical receiver.

The optical fiber 112 comprises one or more fiber optic strands, each ofwhich is made from quartz glass (amorphous SiO₂). The fiber opticstrands are doped with a rare earth compound (such as germanium,praseodymium, or erbium oxides) to alter their refractive indices,although in different embodiments the fiber optic strands may not bedoped. Single mode and multimode optical strands of fiber arecommercially available from, for example, Corning® Optical Fiber.Example optical fibers include ClearCurve™ fibers (bend insensitive),SMF28 series single mode fibers such as SMF-28 ULL fibers or SMF-28efibers, and InfiniCor® series multimode fibers.

The interrogator 106 generates sensing and reference pulses and outputsthe reference pulse after the sensing pulse. The pulses are transmittedalong optical fiber 112 that comprises a first pair of fiber Bragggratings (FBGs). The first pair of FBGs comprises first and second FBGs114 a,b (generally, “FBGs 114”). The first and second FBGs 114 a,b areseparated by a certain segment 116 of the optical fiber 112 (“fibersegment 116”). The length of the fiber segment 116 varies in response toan acoustic vibration that the optical fiber 112 experiences. Each fibersegment 116 between any pair of adjacent FBGs 114 with substantiallyidentical center wavelengths is referred to as a “channel” of the system200.

The light pulses have a wavelength identical or very close to the centerwavelength of the FBGs 114, which is the wavelength of light the FBGs114 are designed to partially reflect; for example, typical FBGs 114 aretuned to reflect light in the 1,000 to 2,000 nm wavelength range. Thesensing and reference pulses are accordingly each partially reflected bythe FBGs 114 a,b and return to the interrogator 106. The delay betweentransmission of the sensing and reference pulses is such that thereference pulse that reflects off the first FBG 114 a (hereinafter the“reflected reference pulse”) arrives at the optical receiver 103simultaneously with the sensing pulse that reflects off the second FBG114 b (hereinafter the “reflected sensing pulse”), which permits opticalinterference to occur.

While FIG. 1 shows only the one pair of FBGs 114 a,b, in differentembodiments (not depicted) any number of FBGs 114 may be on the fiber112, and time division multiplexing (“TDM”) (and optionally, wavelengthdivision multiplexing (“WDM”)) may be used to simultaneously obtainmeasurements from them. If two or more pairs of FBGs 114 are used, anyone of the pairs may be tuned to reflect a different center wavelengththan any other of the pairs. Alternatively a group of multiple FBGs 114may be tuned to reflect a different center wavelength to another groupof multiple FBGs 114 and there may be any number of groups of multipleFBGs extending along the optical fiber 112 with each group of FBGs 114tuned to reflect a different center wavelength. In these exampleembodiments where different pairs or group of FBGs 114 are tuned toreflect different center wavelengths to other pairs or groups of FBGs114, WDM may be used in order to transmit and to receive light from thedifferent pairs or groups of FBGs 114, effectively extending the numberof FBG pairs or groups that can be used in series along the opticalfiber 112 by reducing the effect of optical loss that otherwise wouldhave resulted from light reflecting from the FBGs 114 located on thefiber 112 nearer to the optical source 101. When different pairs of theFBGs 114 are not tuned to different center wavelengths, TDM issufficient.

The interrogator 106 emits laser light with a wavelength selected to beidentical or sufficiently near the center wavelength of the FBGs 114that each of the FBGs 114 partially reflects the light back towards theinterrogator 106. The timing of the successively transmitted lightpulses is such that the light pulses reflected by the first and secondFBGs 114 a,b interfere with each other at the interrogator 106, and theoptical receiver 103 records the resulting interference signal. Theacoustic vibration that the fiber segment 116 experiences alters theoptical path length between the two FBGs 114 and thus causes a phasedifference to arise between the two interfering pulses. The resultantoptical power at the optical receiver 103 can be used to determine thisphase difference. Consequently, the interference signal that theinterrogator 106 receives varies with the acoustic vibration the fibersegment 116 is experiencing, which allows the interrogator 106 toestimate the magnitude of the acoustic vibration the fiber segment 116experiences from the received optical power. The interrogator 106digitizes the phase difference and outputs an electrical signal (“outputsignal”) whose magnitude and frequency vary directly with the magnitudeand frequency of the acoustic vibration the fiber segment 116experiences.

The signal processing device (controller) 118 is communicatively coupledto the interrogator 106 to receive the output signal. The signalprocessing device 118 includes a processor 102 and a non-transitorycomputer readable medium 104 that are communicatively coupled to eachother. An input device 110 and a display 108 interact with the processor102. The computer readable medium 104 has encoded on it statements andinstructions to cause the processor 102 to perform any suitable signalprocessing methods to the output signal. Example methods include thosedescribed in PCT application PCT/CA2012/000018 (publication number WO2013/102252), the entirety of which is hereby incorporated by reference.

FIG. 2 depicts how the FBGs 114 reflect the light pulse, according toanother embodiment in which the optical fiber 112 comprises a third FBG114 c. In FIG. 2, the second FBG 114 b is equidistant from each of thefirst and third FBGs 114 a,c when the fiber 112 is not strained. Thelight pulse is propagating along the fiber 112 and encounters threedifferent FBGs 114, with each of the FBGs 114 reflecting a portion 115of the pulse back towards the interrogator 106. In embodimentscomprising three or more FBGs 114, the portions of the sensing andreference pulses not reflected by the first and second FBGs 114 a,b canreflect off the third FBG 114 c and any subsequent FBGs 114, resultingin interferometry that can be used to detect an acoustic vibration alongthe fiber 112 occurring further from the optical source 101 than thesecond FBG 114 b. For example, in the embodiment of FIG. 2, a portion ofthe sensing pulse not reflected by the first and second FBGs 114 a,b canreflect off the third FBG 114 c and a portion of the reference pulse notreflected by the first FBG 114 a can reflect off the second FBG 114 b,and these reflected pulses can interfere with each other at theinterrogator 106.

Any changes to the optical path length of the fiber segment 116 resultin a corresponding phase difference between the reflected reference andsensing pulses at the interrogator 106. Since the two reflected pulsesare received as one combined interference pulse, the phase differencebetween them is embedded in the combined signal. This phase informationcan be extracted using proper signal processing techniques, such asphase demodulation. The relationship between the optical path of thefiber segment 116 and that phase difference (θ) is as follows: θ=2πnL/λ,where n is the index of refraction of the optical fiber; L is theoptical path length of the fiber segment 116; and λ is the wavelength ofthe optical pulses. A change in nL is caused by the fiber experiencinglongitudinal strain induced by energy being transferred into the fiber.The source of this energy may be, for example, an object outside of thefiber experiencing dynamic strain, undergoing vibration, emitting energyor a thermal event.

One conventional way of determining ΔnL is by using what is broadlyreferred to as distributed acoustic sensing (“DAS”). DAS involves layingthe fiber 112 through or near a region of interest (e.g. a pipeline) andthen sending a coherent laser pulse along the fiber 112. As shown inFIG. 3, the laser pulse interacts with impurities 113 in the fiber 112,which results in scattered laser light 117 because of Rayleighscattering. Vibration or acoustics emanating from the region of interestresults in a certain length of the fiber becoming strained, and theoptical path change along that length varies directly with the magnitudeof that strain. Some of the scattered laser light 117 is back scatteredalong the fiber 112 and is directed towards the optical receiver 103,and depending on the amount of time required for the scattered light 117to reach the receiver and the phase of the scattered light 117 asdetermined at the receiver, the location and magnitude of the vibrationor acoustics can be estimated with respect to time. DAS relies oninterferometry using the reflected light to estimate the strain thefiber experiences. The amount of light that is reflected is relativelylow because it is a subset of the scattered light 117. Consequently, andas evidenced by comparing FIGS. 1B and 1C, Rayleigh scattering transmitsless light back towards the optical receiver 103 than using the FBGs114.

DAS accordingly uses Rayleigh scattering to estimate the magnitude, withrespect to time, of the acoustic vibration experienced by the fiberduring an interrogation time window, which is a proxy for the magnitudeof the acoustic vibration. In contrast, the embodiments described hereinmeasure acoustic vibrations experienced by the fiber 112 usinginterferometry resulting from laser light reflected by FBGs 114 that areadded to the fiber 112 and that are designed to reflect significantlymore of the light than is reflected as a result of Rayleigh scattering.This contrasts with an alternative use of FBGs 114 in which the centerwavelengths of the FBGs 114 are monitored to detect any changes that mayresult to it in response to strain. In the depicted embodiments, groupsof the FBGs 114 are located along the fiber 112. A typical FBG can havea reflectivity rating of 2% or 5%. The use of FBG-based interferometryto measure interference causing events offers several advantages overDAS, in terms of optical performance.

Now turning to FIG. 4, there is shown a modular assembly 200 fordeployment of optical fiber along a pipeline, in accordance with anembodiment of the disclosure. Modular assembly 200 comprises asubterranean pipeline 202 extending beneath ground 204. A line ofconduits 206 extends parallel to pipeline 202, with pairs of adjacentconduits 206 arranged end-to-end. Conduits 206 are positioned withinacoustic proximity (for example 1 meter or less) of pipeline 202, suchthat acoustic events originating from pipeline 202 will reach one ormore of conduits 206 without substantially complete energy loss. While aseparation of 1 meter or less between conduits 206 and pipeline 202generally provides for ideal data acquisition, it is possible forconduits 206 to be positioned further away from pipeline 202. In someembodiments, conduits 206 may be manually placed in a trench directlyon, or buried near, pipeline 202. For example, in some embodimentsconduits 206 may be placed on an outside surface of pipeline 202. It mayalso be possible to use a side boom to lower pipeline 202 and conduit206 into the trench simultaneously. In the present embodiment, eachconduit 206 is about 2 km in length, although greater or smaller lengthsare possible. In some embodiments, different conduits 206 may havedifferent lengths.

Although not shown in FIG. 4, each conduit 206 comprises an opticalfiber disposed therein. Each pair of opposing ends of adjacent conduits206 is connected together by a separate splice box 208. The opticalfibers disposed within each pair of adjacent conduits 206 are opticallyconnected together via the splice box 208 connecting together the pairof adjacent conduits 2016 so as to form a light path through the line ofconduits 206. Although not shown in FIG. 4, the optical fibers disposedwithin each of the conduits 206 comprise at least one pair of fiberBragg gratings, for example as described above in connection with FIGS.1-3. Modular assembly 200 further comprises a data acquisition box 210similar to signal processing device 118 described above. The opticalfiber disposed within conduit 206 furthest from data acquisition box 210terminates in a termination point 212 configured such that lightreaching termination point 212 is absorbed and not reflected back downthe optical fiber.

Turning to FIG. 5, there is shown another embodiment of a modularassembly 300 for deployment of optical fiber along a pipeline. In thisembodiment, in addition to sensing optical fibers comprising FBGs asdescribed above, modular assembly 300 includes a number of serviceoptical fibers (i.e. non-sensing optical fibers) for maximizing dataquality. As seen in FIG. 5, non-sensing optical fibers include lead-inoptical fibers 306 a-c and return optical fibers 308 a-c. Lead-inoptical fibers 306 a-c are optically coupled to corresponding returnoptical fibers 308 a-c via splice boxes 310. At each splice box 310, oneof lead-in optical fibers 306 a-c is further optically connected to acorresponding sensing optical fiber 310 a-c deployed within conduit (notshown, though as described above in connection with FIG. 4). Sensingoptical fibers 310 a-c include fiber Bragg gratings 316 as describedabove. Each splice box 310 comprises a circulator 318 operable to directlight from one of lead-in optical fibers 306 a-c to a respective one ofsensing optical fibers 310 a-c, and to direct light reflected by fiberBragg gratings 316 from sensing optical fibers 310 a-c to return opticalfibers 308 a-c.

An optical interrogator 302 is optically coupled, via a transmissioncoupler 304, to lead-in optical fibers 306 a-c. Transmission coupler 304is optically coupled to lead-in optical fibers 306 a-c such that opticalinterrogator 302 is operable to transmit light into lead-in opticalfibers 306 a-c. Optical interrogator 302 is further optically coupled,via a receiver coupler 314, to return optical fibers 308 a-c. Receivercoupler 314 is optically coupled to return optical fibers 308 a-c suchthat optical interrogator 302 is operable to detect from return opticalfibers 308 a-c the transmitted light which has been reflected by fiberBragg gratings 316.

While the embodiment of FIG. 5 shows three lead-in optical fibers, threereturn optical fibers, and three sensing optical fibers, the number ofoptical fibers may be increased or decreased, and in so doing the numberof splice boxes and circulators may also be accordingly increased ordecreased. In order to assist with positioning of the optical fibers,one or more of conduits 206 may be divided into multiple separatechannels, and each channel may be dimensioned to carry a separateoptical fiber (for example each channel may carry a lead-in opticalfiber, a return optical fiber or a sensing optical fiber).

Advantageously, with either of the modular assemblies described above,relatively easy replacement of a defective optical fiber may be carriedout, without having to remove the entire line of optical fiber. Should alength of optical fiber be found defective, then the optical fiber isdisconnected from its splice boxes. The optical fiber is then removedfrom the conduit, and a replacement optical fiber is deployed within theconduit and optically connected to the splice boxes connected at eitherend of the conduit.

Various methods may be used in order to insert or otherwise deploy theoptical fiber within a conduit. In one example, as shown in FIG. 6, afiberglass rod 602 may be inserted into conduit 604 using acable-jetting device (for example using the optical fiber injectordescribed below). Rod 602 may then be used to pull optical fiber 606. Inthis method, fiberglass rod 602 and optical fiber 606 are attachedtogether in a tip-to-tale fashion, via use of a pre-installed pull tape608. In an alternative embodiment, shown in FIG. 7, fiberglass rod 702is pre-taped to optical fiber 706, approximately every 10 m (thoughother distances may be used). This ensures that optical fiber 706 doesnot experience too much strain while being pulled. Fiberglass rod 702and optical fiber 706 are then jetted simultaneously into conduit 704using a cable-jetting device, for example the optical fiber injectordescribed below.

There will now be described a particular method of deploying opticalfiber within a conduit. Such a method may be used to deploy opticalfiber within one or more conduits forming part of either of the modularassemblies described above in connection with FIGS. 4 and 5. In general,this method of deploying optical fiber uses an optical fiber injector toinject the optical fiber, using pressurized air, into the conduit.

Turning to FIG. 8, there is shown an embodiment of an optical fiberinjector 800 in accordance with an embodiment of the disclosure.Injector 800 is formed from a cylindrical pressure vessel 802 sealableby a removable cover 804. Extending away from pressure vessel 802 in alargely tangential direction is a tapered snout 808 terminating in anair outlet 810. A number of ports 812 are provided in cover 804 to allowfor the injection of pressurized air into pressure vessel 802. Arotatable spool 822 is provided within pressure vessel 802, and ismounted on a shaft 820 extending through pressure vessel 802. Rotationof shaft 820 results in corresponding rotation of spool 822.

Turning to FIG. 9, there is shown a diagram of how injector 800functions in practice. Injector 800 is positioned such that air outlet810 sealingly engages with an open end 812 of conduit 814. A compressor816 is coupled to ports 812 on injector 800 such that air compressor mayinject or otherwise supply compressed air into pressure vessel 802. Adrive mechanism such as a motor 818 is coupled to a shaft 820 runningthough pressure vessel 802. On shaft 820 is provided spool 822 withoptical fiber cable 824 wound thereon. Operation of motor 818 causesshaft 820 to rotate, resulting in corresponding rotation of spool 822and unwinding of optical fiber cable 824 from spool 822. An opticalfiber piston 826 is attached to the end of optical fiber cable 824.Piston 826 is sized and dimensioned to be movable through conduit 814.Should conduit 814 include any bends, then piston 826 is preferablysized and dimensioned to be able to move past any such bends withoutbecoming stuck in conduit 814. As seen by the direction of arrows inFIG. 9, injected pressurized air is directed around cylindrical pressurevessel 802 and towards air outlet 810, where acts on piston 826 andthereby urges piston 826 into and along conduit 814. Consequently,optical fiber cable 824 is urged into and along conduit 814. In someembodiments, it may be possible to jet optical fiber cable 824 withinthe conduit without the assistance of piston 826. This may be the caseif, for example, optical fiber cable 824 comprises sufficient rigidity.

In order to assist with deployment of optical fiber cable 824 withinconduit 814, optical fiber cable 824 preferably comprises reinforcedfiber in addition to optical fiber. For example, optical fiber cable 824may comprise a 1000 d aramid fiber built in beside the optical fiber, inorder to offer additional pull strength. Furthermore, an outer coatingof Hytrel® may be applied to the optical fiber, and a fluorinatedethylene propylene top coat may also be applied, which may increase thelubricity of optical fiber cable 824. Thus, optical fiber cable 824 maycomprise improved stiffness and structure while remaining relativelythin at about 0.002″ in diameter.

Turning to FIGS. 10 and 11, there are shown a method 1100 and system1000 for deploying optical fiber within a conduit, in accordance with anembodiment of the disclosure. Method 1100 uses optical fiber injector800 described above, though other injectors may be used provided thatthey operate within the bounds set out by the appended claims. Method1100 of FIG. 11 includes the jetting of a pull string into the conduit,prior to jetting of the optical fiber cable. Although it is possible todeploy the optical fiber cable without use of a pull string, use of thepull string may be preferable as it may assist with deployment of theoptical fiber cable within the conduit.

Method 1100 begins by jetting a pull string 1002 into conduit 814. Pullstring 1002 comprises a flexible elongate member such as grip-tightweather-resistant twine. In one embodiment, pull string has a diameterof 1.27 mm, a breaking strength 130 lbs, and is procured frommcmaster.com, part number 078T11. Pull string 1002 has a length greaterthan that of conduit 814. Jetting of pull string 1002 into conduit 814is similar to jetting of optical fiber cable 824 into conduit 814, andtherefore, in order to describe jetting of pull string 1002, referenceis also made to FIG. 9. In order to jet pull string 1002, at step 1102 aspool of pull string 1002 is loaded into a pull string injector. Opticalfiber injector 800 may be used as the pull string injector, in whichcase a spool of pull string 1002 is loaded onto shaft 820. At step 1104,a pull string piston is attached to an end of pull string 1002. The pullstring piston may be similar to optical fiber piston 826, and thereforein what follows the pull string piston is also referred to by referencenumeral 826. Pull string piston 826 is configured in size and shape tobe movable through conduit 814 without becoming stuck in any bends inconduit 814. Pull string piston 826 may be secured to pull sting 1002using an appropriate adhesive, such as electrical tape. A tension of upto 100 lbs may be applied to pull string piston 826 to test theattachment of pull string piston 826 to pull string 1002. Pull stringpiston 826 may be coated in a lubricant to assist passage throughconduit 814.

At step 1106, pull string piston 826 is inserted into open end 812 ofconduit 814, and open end 812 of conduit 814 is then sealingly engagedwith air outlet 810 of injector 800. Compressor 816 is then coupled topressure vessel 802 via one or more of ports 812. A manifold (not shown)is used to monitor and control the pressure of air flowing into pressurevessel 802. At step 1108, using compressor 816, pressurized air isinjected into pressure vessel 802 and acts on pull string piston 826 soas to urge pull string piston 826 along conduit 814, thereby jettingpull string 1002 along conduit 814. Progress of the jetting of pullstring 1002 may be monitored via a window on tapered snout 808 ofinjector 800. A typical jetting speed is 5 m/s but can vary depending onthe length of the conduit and the number of bends in the conduit. Atstep 1110, pull string piston 826 is received at the opposite open end830 of conduit 814. At step 1112, pull string 1002 is then coupled tooptical fiber puller or retractor 832, which as described below assistswith the subsequent jetting of optical fiber cable 824.

Once pull string 1002 has been deployed within conduit 814, the methodproceeds to a series of steps in which optical fiber cable 824 is jettedinto conduit 814. In order to jet optical fiber cable 824, at step 1114a spool 822 of optical fiber cable 824 (such as the reinforced opticalfiber cable described above) is loaded into pull string injector 800, byloading spool 822 onto shaft 820. At step 1116, an optical fiber piston(such as the optical fiber piston 826 shown in FIG. 9) is attached to anend of optical fiber cable 824. Optical fiber piston 826 is configuredin size and shape to be movable through conduit 814 without becomingstuck in any bends in conduit 814. At step 1118, optical fiber piston826 is also attached to the end of pull string 1002 that remains on thesending side of system 1000. Optical fiber piston 826 may be secured topull string 1002 using an appropriate adhesive, such as electrical tape.Thus, optical fiber cable 824 and pull string 1002 are attachedend-to-end, with optical fiber piston 826 between them. At step 1120,optical fiber piston 826 is inserted into open end 812 of conduit 814.At step 1122, using compressor 816, pressurized air is injected intopressure vessel 802 and acts on optical fiber piston 826 so as to urgeoptical fiber piston 826 along conduit 814, thereby jetting opticalfiber cable 824 along conduit 814. Progress of the jetting of opticalfiber cable 824 may be monitored via the window on tapered snout 808 ofinjector 800.

During jetting, at step 1124, drive mechanism 818 is operated so as torotate spool 822 and unwind optical fiber cable 824 therefrom. Unwindingoptical fiber cable 824 in this manner assists with the jetting ofoptical fiber cable 824 along conduit 814. To further assist jetting ofoptical fiber cable 824, as can be seen in FIG. 11, on the receivingside of system 1000 is located optical fiber puller or retractor 832.Optical fiber retractor 832 is configured to maintain a tension on pullstring 1002 during jetting of optical fiber cable 824. Optical fiberretractor 832 includes a load monitor so that the operator may ensurethat optical fiber cable 824 is not subjected to undue loads duringjetting. In other embodiments, suction may be applied at the open end ofconduit 814 on the receiving side, to assist in jetting of optical fibercable 824. For example, an industrial vacuum pump may be coupled to theopen end of conduit 814 on the receiving side, and may suck air out ofconduit 814 during jetting of optical fiber cable 824.

At step 1126, once optical fiber piston 826 is received at the receivingside of system 1000, optical fiber cable 824 is determined to have beensuccessfully deployed within conduit 814. The optical fiber comprised inoptical fiber cable 824 may then be optically coupled to splice boxesand/or transmission/return couplers as described above. Should opticalfiber cable 824 need to be removed from conduit 814, then a piston asdescribed above may be attached to optical fiber cable 824, and opticalfiber cable 824 may be jetted out of conduit 814, also as describedabove.

One or more example embodiments have been described by way ofillustration only. This description has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the form disclosed. Many modifications and variations will beapparent to those of ordinary skill in the art without departing fromthe scope of the claims. It will be apparent to persons skilled in theart that a number of variations and modifications can be made withoutdeparting from the scope of the claims. For example, in someembodiments, the pull string may be pre-deployed within the conduit, orthe optical fiber may be jetted without use of a pull string.

It is furthermore contemplated that any part of any aspect or embodimentdiscussed in this specification can be implemented or combined with anypart of any other aspect or embodiment discussed in this specification.

1. A modular assembly for deployment of optical fiber along a pipeline,the modular assembly comprising: a pipeline; and a line of two or moreconduits arranged end-to-end, each pair of opposing ends of adjacentconduits being connected together by a separate splice box, wherein theline is positioned along and adjacent to a length of the pipeline. 2.The modular assembly of claim 1, further comprising an optical fiberdisposed within each of the conduits.
 3. The modular assembly of claim2, wherein the optical fibers disposed within each pair of adjacentconduits are optically connected together via the splice box connectingtogether the pair of adjacent conduits so as to form a light paththrough the line.
 4. The modular assembly of claim 3, wherein theoptical fiber disposed within each of the conduits comprises at leastone pair of fiber Bragg gratings.
 5. The modular assembly of claim 4,further comprising an optical interrogator optically coupled to theoptical fiber disposed within the conduit at an input end of the line,the optical interrogator being operable to transmit light into theoptical fiber disposed within the conduit at the input end, and theoptical interrogator being operable to receive from the optical fiberdisposed within the conduit at the input end the transmitted light whichhas been reflected by the at least one pair of fiber Bragg gratings. 6.The modular assembly of claim 5, further comprising an absorption unitoptically coupled to the optical fiber disposed within the conduit at anabsorption end of the line, the absorption unit being operable to absorblight output from the optical fiber disposed within the conduit at theabsorption end so as to prevent the output light reflecting back intothe optical fiber disposed within the conduit at the absorption end. 7.The modular assembly of claim 6, further comprising an additionaloptical fiber disposed within each of a plurality of the conduits, theplurality forming an unbroken portion of the line and including theconduit at the input end, wherein the additional optical fibers areoptically connected together via the splice boxes connecting togetherthe plurality of the conduits so as to form an additional light paththrough at least a portion of the line, and wherein the additionaloptical fiber disposed within the conduit at the input end is opticallycoupled to the optical interrogator.
 8. The modular assembly of 7,wherein the plurality of the conduits includes all of the conduits ofthe line, and wherein the additional optical fiber disposed within theconduit at the absorption end is optically coupled to the absorptionunit.
 9. The modular assembly of claim 1, wherein at least one of thesplice boxes connecting together a pair of adjacent conduits comprises acirculator; wherein the one conduit of the pair of adjacent conduitsclosest an input end of the line comprises a lead-in optical fiber and aseparate return optical fiber, the lead-in and return optical fibersbeing optically coupled to the circulator; wherein the one conduit ofthe pair of adjacent conduits closest an absorption end of the linecomprises a sensing optical fiber optically coupled to the circulatorand comprising a pair of fiber Bragg gratings; and wherein thecirculator is operable to direct light from the lead-in optical fiber tothe sensing optical fiber, and to direct light reflected by the pair offiber Bragg gratings from the sensing optical fiber to the returnoptical fiber.
 10. The modular assembly of claim 9, further comprisingan optical interrogator having a transmission coupler and a receivercoupler, the transmission coupler being optically coupled to the lead-inoptical fiber such that the optical interrogator is operable to transmitlight into the lead-in optical fiber, and the receiver coupler beingoptically coupled to the return optical fiber such that the opticalinterrogator is operable to detect from the return optical fiber thetransmitted light reflected by the pair of fiber Bragg gratings.
 11. Themodular assembly of claim 10, wherein an additional one of the spliceboxes connecting together an additional pair of adjacent conduitscomprises an additional circulator; wherein the one conduit of theadditional pair of adjacent conduits closest an input end of the linecomprises an additional lead-in optical fiber and a separate additionalreturn optical fiber, the additional lead-in and additional returnoptical fibers being optically coupled to the additional circulator;wherein the one conduit of the additional pair of adjacent conduitsclosest an absorption end of the line comprises an additional sensingoptical fiber optically coupled to the additional circulator andcomprising an additional pair of fiber Bragg gratings; and wherein theadditional circulator is operable to direct light from the additionallead-in optical fiber to the additional sensing optical fiber, and todirect light reflected by the additional pair of fiber Bragg gratingsfrom the additional sensing optical fiber to the additional returnoptical fiber.
 12. The modular assembly of claim 1, wherein at least oneof the conduits of the line is divided into multiple separate channels,each channel being dimensioned to carry a separate optical fiber. 13.The modular assembly of claim 1, wherein one of the conduits of the linecomprises a rod or tape releasably fixed to an internal surface of theone conduit.
 14. The modular assembly of claim 1, wherein each conduitis made from a stainless steel capillary tube.
 15. The modular assemblyof claim 1, wherein the line is positioned within one meter of thelength of the pipeline.
 16. The modular assembly of claim 15, whereinthe line is fixed to an outer surface of the length of the pipeline. 17.A method for deploying optical fiber along a pipeline, the methodcomprising: installing a modular assembly along and adjacent to a lengthof the pipeline, the modular assembly comprising a line of two or moreconduits arranged end-to-end, each pair of opposing ends of adjacentconduits being connected together by a separate splice box; disposingoptical fiber within each conduit of the installed modular assembly; andoptically connecting together the optical fibers disposed within eachpair of adjacent conduits via the splice box connecting together thepair of adjacent conduits.
 18. The method of claim 17, whereininstalling the modular assembly comprises coupling the modular assemblyto the length of the pipeline prior to installation of the pipeline suchthat the modular assembly is installed with the pipeline.
 19. The methodof claim 17, wherein installing the modular assembly comprisespositioning the modular assembly within one meter of the length of thepipeline after the pipeline has been installed.
 20. The method of claim17, wherein installing the modular assembly comprises fixing at leastone conduit of the modular assembly to an outer surface of the length ofthe pipeline.
 21. The method of claim 17, wherein disposing opticalfiber into each conduit comprises pushing at least one optical fiberthrough at least one conduit using a cable-jetting device or a spoolingdevice.
 22. The method of claim 17, wherein disposing optical fiber intoeach conduit comprises pulling at least one optical fiber through atleast one conduit using a rod or tape, wherein the rod or tape isconnected to the at least one optical fiber and extends through amajority of the at least one conduit.
 23. The method of claim 22,wherein the rod or tape is releasably fixed to an internal surface ofthe at least one conduit prior to being used to pull the at least oneoptical fiber through the at least one conduit.
 24. The method of claim17, wherein the disposing of optical fiber into at least one of theconduits comprises: providing an optical fiber injector comprising apressure vessel having a fluid inlet and a fluid outlet; engaging thefluid outlet with an open end of a conduit; providing a length ofoptical fiber within the pressure vessel; and jetting the optical fiberinto the conduit by injecting a fluid into the pressure vessel via thefluid inlet, wherein the optical fiber injector is configured such thatthe fluid is directed from the fluid inlet to the fluid outlet, andurges the optical fiber to move through the conduit, thereby deployingthe optical fiber within the conduit.
 25. The method of claim 17,further comprising: disconnecting an optical fiber disposed within oneof the conduits from the splice boxes connected at either end of the oneconduit; removing the disconnected optical fiber from the one conduit;disposing a replacement optical fiber within the one conduit andoptically connecting the replacement optical fiber to the splice boxesconnected at either end of the one conduit.
 26. The method of claim 25,further comprising determining that the optical fiber is malfunctioningprior to disconnecting the optical fiber.